Audio Control Output

A project log for Zappotron Super-Sequencer

NES Zapper Controlled drum sequencer

Russell KramerRussell Kramer 03/22/2017 at 03:260 Comments

The drum step counter is slowly counting from 0-15. I need to get the voltages out of the capacitor demultiplexers that match this index so they can control audio generating circuits. The problem is the capacitor demultiplexers is already being addressed by the draw step count which cycles from 0-15 sixty times a second. I can't change this without losing the indication dots on the TV.

The solution is to take advantage of the 74LS85 output used to produce an indication bar and add a set of sample-and-hold circuits. One of the 16 steps being drawn on the screen matches the drum step count. If I only allow a capacitor to charge from the demultiplexer output during this period it will take the voltage of the capacitor in the demultiplexer that matches the drum step count.

I'm adding the control to run the tape drive motors at this point too. Outputs destined for motors are voltage followers with a 2N3904 current boost. Outputs going to 4046 VCOs are regular opamp buffers. An LM324 audio op-amp is used here because it doesn't need to handle a high frequency video rate signal.